The present invention relates to energetic polyester thermoplastic homopolymers and more particularly to the synthesis thereof and to energetic copolyether-ester thermoplastic elastomers obtained therefrom.
High-energy solid compositions such as propellants and composite explosives are usually prepared by combining a variety of materials including oxidizers, binders, plasticizers and a curing agent. Many energetic binders are available for use in the preparation of these high-energy compositions. Usually, these binders are obtained by a curing reaction involving the use of isocyanates and polyhydroxyl energetic or non energetic prepolymers. The binders give the insensitive character to high energy compositions. For composite explosives, the use of these binders leads to plastic bounded explosives (PBXs), which are chemically crosslinked and not recyclable. Moreover, the existing melt cast facilities are not suitable for cast-cured PBX. An elegant way to formulate PBXs in available melt cast facilities is to use thermoplastic elastomers. Moreover, an advantage of using thermoplastic elastomers is that they lead to recyclable PBXs. Furthermore, it would be more desirable to use energetic thermoplastic elastomers because replacing explosives by energetic binders in the composition results in a lesser loss of energy in comparison with non energetic binders. The limitation of this technology is that thermoplastic elastomers melting in the range of between 80xc2x0 C. and 100xc2x0 C. are needed in order to be processed in the existing melt-cast facilities and that those melting at higher temperatures are not suitable for this process. For years, researchers have tried to synthesize energetic thermoplastic elastomers melting between 80xc2x0 C. and 100xc2x0 C. In U.S. Pat. No. 4,707,540, issued to Manser, in 1987, it was established that the polymerization of numerous oxetane monomers yielded energetic homopolymers that could be used as binders. Among these oxetane polymers, Manser isolated BAMO, an energetic thermoplastic homopolymer which melts at 83xc2x0 C. Until now BAMO was the only available energetic thermoplastic homopolymer.
U.S. Pat. No. 4,806,613, issued to Wardle, in 1989, showed that energetic thermoplastic elastomers could be prepared directly in the mixer by block polymerization of BAMO with other oxetane polymers.
Wardle also showed in U.S. Pat. No. 4,952,644, that ABA triblocks or star thermoplastic elastomers could be obtained by polymerization of the BAMO monomers with other oxetanes monomers. Although useful, all these energetic thermoplastic elastomers must comprise BAMO as the hard segment. Since energetic thermoplastic elastomers are potential products to introduce in and prepare insensitive high-energy compositions, there is a need to develop new energetic thermoplastic homopolymers and energetic thermoplastic elastomers.
An object of one embodiment of the present invention is to provide the synthesis of novel energetic polyester thermoplastic homopolymers by the polymerization of xcex1-bromomethyl-xcex1-methyl-xcex2-propiolactone (BMMPL) or xcex1-chloromethyl-xcex1-methyl-xcex2-propiolactone (CMMPL) to yield thermoplastic homopolymers which upon azidation, lead to a novel energetic thermoplastic polyester: poly(xcex1-azidomethyl-xcex1-methyl-xcex2-propiolactone) (PAMMPL).
A further object of the embodiment of the present invention is an energetic thermoplastic polyester of the formula: 
where n is 4 to 1500. This new energetic polyester melts at 80xc2x0 C. and can be used as the hard block of an energetic thermoplastic elastomer.
Another object of this invention is to provide a process to synthesize energetic copolyether-ester thermoplastic elastomers and particularly those copolyether-esters that are obtained by using energetic dihydroxyl terminated prepolymers such as glycidyl azide polymer as macroinitiators for the polymerization of xcex1-bromomethyl-xcex1-methyl-xcex2-propiolactone (BMMPL) or xcex1-chloromethyl-xcex1-methyl-xcex2-propiolactone (CMMPL) followed by the azidation of the resulting copolymers. The resulting copolyether-esters are energetic thermoplastic elastomers, which melt at 80xc2x0 C.
Another object of the present invention is also to provide the synthesis of a novel energetic polyester homopolymer by the polymerization of xcex1-dibromomethyl-xcex2-propiolactone (DBMPL) to yield an homopolymer which upon azidation, led to a novel energetic polyester: poly(xcex1-diazidomethyl-xcex2-propiolactone) (PDAMPL). This new energetic polyester can be used as a binder or be introduced in an energetic thermoplastic elastomer synthesis. 
Where n could be 3 to 1100 leading to molecular weights between 500 to 200 000 g/mol.
In accordance with another feature of the present invention, there is provided a process for preparing an energetic copolyether-ester thermoplastic elastomer of type ABA. This process comprises the step of using an energetic dihydroxyl terminated polymer as a macroinitiator to polymerize xcex1-bromomethyl-xcex1-methyl-xcex2-propiolactone (BMMPL) or xcex1-chloromethyl-xcex1-methyl-xcex2-propiolactone (CMMPL) followed by the azidation of the resulting copolymer. The structure of the resulting copolyether-ester can be illustrated as followed:
PAMMPL-DHTEP-PAMMPL
where PAMMPL is the hard polyester block A and DHTEP is the dihydroxyl terminated polyether used as the soft block B. Preferably, the dihydroxyl terminated energetic polymer (soft segment) has a molecular weight ranging from about 500 to about 100,000 g/mol and the PAMMPL (hard segment) has a molecular weight of 500 to 200,000 g/mol. Preferably, the dihydroxyl terminated prepolymer is glycidyl azide polymer (GAP), but is not limited to and could be applied to other hydroxyl terminated energetic prepolymer selected from the group consisting of: poly 3-azidomethyl-3-methyloxetane (AMMO), poly 3-nitratomethyl-3-methyloxetane (NIMMO) and poly glycidyl nitrate (GLYN).
Those skilled in the art will see that the functionality of the soft segment is not restricted to two. In fact, using the process with a difunctional soft segment resulted in an ABA triblock copolymer but using a monofunctional soft segment would have resulted in an AB diblock copolymer. The use of a tri-, tetra- or polyfunctional soft segment would have led to star shaped or grafted thermoplastic elastomers.
Yet another object of one embodiment of the present invention is to provide an energetic for use as a prepolymer for binder or thermoplastic elastomer synthesis having the formula: 
Where n could be 3 to 1100 leading to molecular weights between 500 to 200 000 g/mol which can be used as a binder or be introduced in an energetic thermoplastic elastomer synthesis.
Having thus generally denoted the invention, reference will now be made to the accompanying drawings.